A wide range of rechargeable batteries is known that can supply an electrical current to drive a load during a discharge process and that can receive electrical current from a charging device to recharge the battery. Examples of rechargeable batteries include, but are not limited to, metal-ion, metal-oxygen, lead acid, rechargeable alkaline, flow batteries, and the like. Examples of metal-ion and metal-oxygen batteries include lithium-ion and lithium-oxygen (sometimes referred to as lithium-air) batteries.
A flow battery is a form of rechargeable battery in which electrolyte containing one or more dissolved electroactive species flows through an electrochemical cell that converts chemical energy directly to electricity. The electrolyte is stored externally, generally in tanks, and is pumped through the cell (or cells) of the reactor. Control of flow batteries requires knowledge of the flow rate and State of Charge (SOC) of the battery. Together these two factors determine the concentration and availability of reactants at the electrodes and the current that can be drawn from the cell for the best efficiency within predetermined operating limits. The SOC is also used to determine how much energy the battery can store or deliver. This variable can be used to plan the usage of the battery in a device or within a power supply system. The identified SOC may also determine the power that the battery can produce at any given time during discharge process.
Many applications that use batteries to supply electrical power benefit from an accurate knowledge of the SOC within the battery during operation. For example, in flow batteries, such as Zinc-Bromine batteries, external or internal sensing devices can detect when the battery is either completely discharged or fully charged with reasonable accuracy. During operation, however, the battery is typically in an intermediate state between being fully charged and fully discharged. Additionally, the battery can be receiving charge or supplying current at different times during operation. Battery sensors, such as current and voltage sensors, do not provide complete information about the battery SOC and analytical or experimentally developed models are often used to compute SOC. Different models are used based on the physical and electrochemical characteristics for a large population of batteries that share a common design. While the models can provide fairly accurate estimates of SOC in a battery that conforms to the predetermined model, an individual battery often deviates from the model due to variations in materials and manufacturing tolerances, environmental conditions in which the battery operates, and physical and electrochemical changes that occur in the battery over the course of multiple charge and discharge cycles. Thus, utilization of fixed models for estimating SOC has drawbacks and requires improvements.
In light of the foregoing limitations in the art, a need exists for improved systems and methods for estimating the SOC in individual batteries. Additionally, improved methods of estimating SOC that are applicable to multiple forms of battery, including metal-ion, metal-air, and flow batteries, would be beneficial.